1. Field of the Invention
The present invention relates to a semiconductor memory device and, for example, to the sense amplifier circuit of a semiconductor memory device having floating body cells.
2. Description of the Related Art
Recently, a memory cell called a floating body cell (FBC) has received attention as a memory cell of a semiconductor memory device (e.g., Takashi Ohsawa et al., “An 18.5 ns 128 Mb SOI DRAM with a Floating Body Cell”, “ISSCC 2005 Digest of Technical Papers”, pp. 458-459). An FBC is formed on a silicon-on-insulator (SOI) substrate. The FBC accumulates charges in an SOI body region and associates the presence/absence of charges with binary digits 1 and 0, thereby storing data. The SOI technology is effective for micropatterning of a semiconductor memory device because the signal does not decrease along with the progress of micropatterning of the device.
The FBC is capable of nondestructive read, although it is volatile and requires refresh. It is also necessary to write back read data because of charge-pumping and the like. Hence, a semiconductor memory device using FBCs requires a sense amplifier that satisfies the above conditions, and sense amplifiers meeting the above requirements have been proposed.